In the fabrication of flexible liquid crystal (LC) displays, electroluminescent devices and photovoltaic cells transparent ITO (indium-tin oxide) electrodes are used. These electrodes are made by vacuum sputtering of ITO onto a substrate. This method involves high temperatures, up to 250° C., and therefore glass substrates are generally used. The range of potential applications is limited, because of the high fabrication costs, the low flexibility (pliability) and stretchability as a consequence of the brittleness of the ITO layer and the glass substrate. Therefore the interest is growing in all-organic devices, comprising plastic resins as a substrate and organic intrinsically conductive polymer layers as electrodes. Such plastic electronics allow the realization of low cost devices with new properties (Physics World, March 1999, p.25-39). Flexible plastic substrates can be provided with an intrinsically conductive polymer layer by continuous roller coating methods (compared to batch process such as sputtering) and the resulting organic electrodes enable the fabrication of electronic devices characterised by a higher flexibility and a lower weight.
The production and the use of intrinsically conductive polymers such as polypyrrole, polyaniline, polyacetylene, polyparaphenylene, polythiophene, polyphenylenevinylene, polythienylenevinylene and polyphenylenesulphide are known in the art.
EP-A 440 957 discloses dispersions of polythiophenes, constructed from structural units of formula (I): in which R1 and R2 independently of one another represent hydrogen or a C1-4-alkyl group or together form an optionally substituted C1-4-alkylene residue, in the presence of polyanions. Furthermore, EP-A-686 662 discloses mixtures of A) neutral polythiophenes with the repeating structural unit of formula (I), in which R1 and R2 independently of one another represent hydrogen or a C1-4-alkyl group or together represent an optionally substituted C1-4-alkylene residue, preferably an optionally with alkyl group substituted methylene, an optionally with C1-12-alkyl or phenyl group substituted 1,2-ethylene residue or a 1,2-cyclohexene residue, and B) a di- or polyhydroxy- and/or carboxy groups or amide or lactam group containing organic compound; and conductive coatings therefrom which are tempered at elevated temperature, preferably between 100 and 250° C., during preferably 1 to 90 seconds to increase their resistance preferably to <300 ohm/square.
EP-A 1 079 397 discloses a method of making an electroconductive pattern on a support which is provided with a polymer layer containing a polythiophene, a polyanion and a di- or polyhydroxy organic compound, wherein the surface resistance (SR) of the polymer layer is reduced at selected areas from an initial value SRi, which is higher than 104 Ω/square, to SRi/Δ, Δ being at least 10, by heating the selected areas without substantially ablating or destroying the polymer layer.
JP 04-100867 discloses a conductive paste characterized in that it is a conductive paste material comprising conductive material, organic binder and solvent as essential components and the volumetric resistance rises through heat treatment after application and drying.
U.S. Pat. No. 5,354,613 discloses a sheet or web material comprising a hydrophobic resin support or paper support coated with at least one hydrophobic resin layer wherein said resin support or resin layer is coated with an outermost antistatic layer containing as an essential component a polythiophene with conjugated polymer backbone in the presence of a polymeric polyanion compound, wherein said antistatic layer contains also a hydrophobic organic polymer having a glass transition value (Tg) of at least 40° C., said polythiophene being present at a coverage of at least 0.001 g/m2 and the weight ratio of said polythiophene to said hydrophobic organic polymer being in the range of 1/10 to 1/1000. The invention examples disclose weight ratios of polythiophene to hydrophobic polymer in the range of 1/18.5 to 1/110.8 in coated dispersions containing N-methylpyrrolidone, an aprotic compound with a dielectric constant, ∈, ≧15, and a weight ratio of polythiophene to hydrophobic polymer of 1/60.5 in dispersions not containing N-methylpyrrolidone.
EP-A 1 054 414 discloses a method for producing electrode pattern in a conductive polymer on a substrate comprising the steps of: applying a layer containing between 10 and 5000 mg/m2 of a conductive polymer, so as to prepare a conductive layer, and printing an electrode pattern on said layer using a printing solution containing of an oxidant selected from the group consisting of ClO−, BrO−, MnO4−, Cr2O7−−, S2O8−− and H2O2. Example 1 discloses the coating of a dispersion containing 417 mL of a PT dispersion containing 0.284% by weight of PEDOT, 50 mL of methylpyrrolidone, an aprotic compound with a dielectric constant, ∈, ≧15, 8.8 mL of a 30% by weight dispersion of co(vinylidene chloride/methyl acrylate/itaconic acid 88/10/2 and 0.5 mL of FLUORAD™ FC430 made up to 1000 mL with distilled water on a 100 μm thick poly(ethylene terephthalate) support. The weight ratio of polythiophene (PEDOT) to polymer was 1/2.15.
EP-A 1 003 179 discloses a method for producing a polymeric conductive layer on an object comprising the steps of: providing an aqueous composition containing a polythiophene, a polyanion compound and an aprotic compound with a dielectric constant, ∈, ≧15; applying said composition to said object forming a layer; and drying said layer to form a conductive polymeric layer on said object. Example 1 discloses the coating of a dispersion containing 417 mL of a PT dispersion containing 0.284% by weight of PEDOT, 50 mL of methylpyrrolidone, an aprotic compound with a dielectric constant, ∈, ≧15, 8.8 mL of a 30% by weight dispersion of co(vinylidene chloride/methyl acrylate/itaconic acid 88/10/2 and 0.5 mL of FLUORAD™ FC430 made up to 1000 mL with distilled water on a 100 μm thick poly(ethylene terephthalate) support. The weight ratio of polythiophene (PEDOT) to polymer was 1/2.15.
Coated layers of organic intrinsically conductive polymers can be structured into patterns using known microlithography techniques. In WO-A-97 18944 a process is described wherein a positive or negative photoresist is applied on top of a coated layer of an organic intrinsically conductive polymer, and after the steps of selectively exposing the photoresist to UV light, developing the photoresist, etching the intrinsically conductive polymer layer and finally stripping the non-developed photoresist with an organic solvent, a patterned layer is obtained. A similar technique has been described in 1988 in Synthetic Metals, volume 22, pages 265-271 for the design of an all-organic thin-film transistor. Such methods are cumbersome as they involve many steps and require the use of hazardous chemicals.